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Thread: 912ULS manifold pressure

  1. #1

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    Default 912ULS manifold pressure

    Ordered an Airmaster prop and thought I would get a head start and install the Grand Rapids manifold pressure sensor. So in checking the Rotax installation manual it suggests a water trap between the engine and sensor. Anyone have any idea what they are talking about? Has anyone installed a water trap between the balance tube and their manifold sensor? An exhaustive search has not found anything like an aircraft manifold pressure water trap. Thanks for any replies.

  2. #2
    Senior Member jrevens's Avatar
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    Default Re: 912ULS manifold pressure

    cposer,

    Similar to a water trap on a natural gas line, or a static line on an aircraft, I suppose it's just a capped-off short section of line, or small container that is connected with a tee fitting to the MP line and oriented to go down from it. Any liquid that may be in the line is then "trapped" in that short line or container before it gets to the sensor. There will also be a plug, cap or valve at the bottom of the trap to empty it if necessary. There may be something made commercially if you Google it. I know that there is a plastic one (used on some Cessnas?) for the static system, but I haven't really heard of one being used on a manifold pressure sensing system. I'm sure someone else is better informed than I about this and will chime in.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE

  3. #3
    Senior Member jiott's Avatar
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    Default Re: 912ULS manifold pressure

    I saw the Rotax recommendation so I installed a trap in my manifold pressure sensor line at the lowest point. I found a small brass tee fitting with 1/4" hose barbs inline and a female 1/8 npt on the tee. I use a 1/8 npt male plug that can easily be removed to drain it. I do it at the yearly annual, but have never had more than 1 drop come out, sometimes none; been in there 7 years now. Probably one of those nice to do things, but not really necessary.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  4. #4
    Senior Member jiott's Avatar
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    Default Re: 912ULS manifold pressure

    Think I found the brass tee at Home Depot but not sure.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  5. #5

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    Default Re: 912ULS manifold pressure

    Thanks, I ordered one from amazon. Are you running a constant speed prop?

  6. #6
    Senior Member jiott's Avatar
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    Default Re: 912ULS manifold pressure

    No, just a ground adjustable fixed. I don't know why I measure MP; its not very useful with a fixed prop.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  7. #7

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    Default Re: 912ULS manifold pressure

    For anyone interested this is what I ended up with for a manifold pressure line water trap. It is an 1/8"x1/8"x1/8"male NPT tee fitting. I then machined a cap with a little reservoir on it.water trap 1.jpgwater trap 2.jpg

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